The effects of tricyclic antidepressants on psychomotor and cognitive functioning are of considerable practical significance particularly in the elderly. It has been reported that up to 30% of geriatric patients treated with a tricyclic antidepressant develop confusion or delirium. However, there are no well controlled studies that have assessed the effects of therapeutic blood levels of a tricyclic antidepressant on performance in the elderly. The current study addresses these concerns by examining the effects of nortriptyline (NT) on human performance. NT is a tricyclic antidepressant with a well established therapeutic window, an absence of marked age- related differences in pharmacokinetics and a more favorable side effects profile. Using a placebo controlled, double-blind, parallel group design, this study will compare the performance of young and elderly depressed in response to a single dose of NT as well as chronic NT treatment at comparable therapeutic plasma levels. The main goals of this study will be: 1) to establish the performance effects of a single dose of NT and to test whether the magnitude of impairment produced by a single dose predicts impairment with continued treatment. 2) to establish the performance effects of chronic treatment at therapeutic plasma levels of NT. 3) to establish whether there is an age-related sensitivity to these effects. 4) to examine the relationship between plasma concentrations of NT and the magnitude of NT's effects on performance. 5) to determine in NT is equally efficacious as an antidepressant in young and old.